PROJECT SUMMARY Neural tube defects (NTD), resulting from a failure in the transformation of a flat neural plate into a closed neural tube, occur in approximately one in every thousand births. When the anterior neural tube fails to close, it results in a fatal birth defect called anencephaly in which the brain and skull fail to develop. Our long- term goal is to use zebrafish to define the genetic and cellular mechanisms that control closure of the anterior neural tube. We found that zebrafish embryos with reduced Nodal signaling have an open anterior neural tube phenotype analogous to anencephaly. Our previous research demonstrated that the role of Nodal signaling is to induce anterior mesodermal and mesendodermal tissues. These tissues then communicate with the overlying neuroepithelium in some way that promotes neural tube closure. The experiments in this proposal will define the steps downstream of Nodal signaling and mesoderm/mesendoderm formation that are required for anterior neurulation. A recent RNAseq screen in the Liang laboratory identified over 3,000 genes that are differentially expressed between embryos with open and closed neural tubes. Many of these genes fall into pathways are good candidates to be working with Nodal signaling to promote neural tube closure. The role of these candidate pathways will be tested through loss-of- function and rescue experiments that will determine whether they are necessary for neural tube closure and whether they interact with Nodal signaling. The second part of this proposal will define defects in the neuroepithelium that prevent it from closing. Biochemical and cellular techniques that measure cell polarity, cell morphology, and protein localization and expression will define the changes that correlate with the open neural tube phenotype. These research goals will be tightly linked to the creation of an ?Experimental Biology? course that will increase the opportunities for undergraduate students to participate in hypothesis-driven, original research. In this course, small groups of undergraduate students will work together to generate a hypothesis on the role of one of the RNAseq candidate genes in anterior neurulation. They will then test their hypothesis by characterizing the neural tube phenotype of a new zebrafish mutant they make using CRISPR/Cas9 genome editing. Anterior neurulation in mammals requires a similar tissue, the head mesenchyme, that also underlies the developing neural tube. Thus, this cooperative research by undergraduate and graduate students has great potential to reveal new genes and signaling pathways that could underlie anencephaly in humans. !